Today is the birthday of George Wald, born in 1906, he discovered that when a pigment in the retina called rhodopsin or visual purple was exposed to light it formed opsin and a compound containing vitamin A. When you go into the dark your eyes become light adapted. This is because visual purple or rhodopsin is being formed in the retina. If the lights come on the visual purple is destroyed and everything is dark again. You have to wait until Opsin and Vitamin A recombine to form Rhodopsin before you can see again.